Lignite Biosolubilization by Bacillus sp. RKB 2 and Characterization of its Products

Nowadays, the advancements of coal microbiology and biotechnology have been highly emphasized, providing leading-edge approaches in sustainable development of agriculture and the protection of the environment. The biosolubilization of low-rank coals, such as lignite and leonardite is a promising technology for converting these sedimentary rocks into valuable products. In this study, the process involved in lignite biosolubilization by Bacillus sp. RKB 2 was investigated. The biotransformed lignite and the produced humic substances were determined in vitro in a liquid medium and on a solid matrix. The bacterial strain was isolated from untreated Kazakhstani lignite and was shown to be capable of effectively solubilizing and transforming lignite (5% w/v). Fourier Transform Infrared (FTIR) and UHPLC-QqQ-MS/MS analyses were performed to examine the solubilization products and lignite humic substances processed by bacteria. The absorption peaks of FTIR showed the diverse nature of the bacteria-induced humic substances, and the vast majority of intense peaks detected are mainly below an m/z of 1000 Da (liquid chromatography-mass spectrometry [LC-MS] (QqQ)). Data analysis concluded that our isolate could depolymerize lignite and form bio-humic substances. Due to its ability to solubilize lignite Bacillus sp. RKB 2 may be useful in the coal-bed for in situ bioutilization of low-rank coal.